Method for producing sodium hydroxide and/or chlorine, and two-chamber type electrolytic cell for saltwater

ABSTRACT

A method for producing sodium hydroxide and/or chlorine by electrolyzing saltwater includes supplying saltwater to an anode chamber of a unit cell in a two-chamber type electrolytic cell, humidifying oxygen-containing gas in a humidifying chamber of the unit cell, and supplying humidified oxygen-containing gas generated in the humidifying chamber to a cathode chamber of the unit cell. The humidifying chamber is adjoined to and in heat exchange relation with the anode chamber or the cathode chamber in the unit cell, or is adjoined to and in heat exchange relation with an anode chamber or a cathode chamber in another unit cell adjacent to the unit cell. The oxygen-containing gas is humidified by generating water vapor with heat from the anode chamber or the cathode chamber adjoined to the humidifying chamber.

TECHNICAL FIELD

One or more embodiments of the present invention relate to a method forproducing sodium hydroxide and/or chlorine, and a two-chamber typeelectrolytic cell for saltwater.

BACKGROUND

Sodium hydrate and chlorine are essential as industrial materials. Theyhave conventionally been produced by a method using an ion exchangemembrane electrolytic cell to electrolyze saltwater, in which a metalelectrode is used as a cathode and the saltwater is electrolyzedaccording to the reaction given by the following equation (1).

2NaCl+2H₂O→Cl₂+2NaOH+H₂  (11)

However, since the electrolysis of saltwater according to the aboveequation (I) requires huge amounts of electric power, a method in whicha gas-diffusion electrode is used as a cathode to reduce oxygen(hereinafter, referred to as oxygen cathode method) has been addressedin hope of significant energy saving in recent years. In the oxygencathode method, a reaction at the anode is oxidation of chlorine ion,which is the same as in the conventional method, and as a whole, thereaction is given by the following equation (2).

2NaCl+½O₂+H₂O→Cl₂+2NaOH  (2)

In the oxygen cathode method, a three-chamber type method, in which anelectrolytic cell is divided into an anode chamber, a catholyte chamber,and a cathode gas chamber, has been employed. However, in recent years,as described in Patent Document 1, for example, a two-chamber typemethod has been investigated, in which an electrolytic cell is dividedinto an anode chamber and a cathode gas chamber by making an anode, anion exchange membrane, and a gas-diffusion cathode attached firmly toeach other to eliminate a catholyte chamber substantially. As shown inthe above chemical equations, water is required for electrolyzingsaltwater, and at the same time, water is also required for keeping theconcentration of the generated sodium hydroxide from being too high. Inthe three-chamber type method, the cathode chamber has a liquid chamberto circulate aqueous sodium hydroxide, from which sufficient water issupplied. On the other hand, in the two-chamber type method, since thecathode chamber does not have a liquid chamber, water is suppliedthrough the ion exchange membrane from the anode chamber aselectro-osmosis water, which is not sufficient, and water is needed tobe supplied to the cathode in some way. The Patent Document 1 disclosesthat the shortage of water is compensated by supplying water through thegas chamber, and specifically discloses that water is heated beforehandto 90° C. and then introduced through an inlet for oxygen gas. PatentDocument 2 also discloses that humidified oxygen-containing gas issupplied to the cathode chamber, and specifically discloses that thehumidified oxygen-containing gas has been prepared by bubbling oxygeninto water heated to 80° C. and then is introduced to the cathodechamber.

PATENT DOCUMENTS

-   Patent Document 1: JP-A-2001-3188-   Patent Document 2: JP-A-H11-152591

However, the method for supplying water disclosed in the Patent Document1 and 2 requires energy to heat water to 80° C. or 90° C. In addition,in the method disclosed in the Patent Document 1, when the temperatureof the electrolytic cell becomes too high, the anolyte temperature isdecreased by circulating the anolyte in an external heat exchanger andusing cooling water and the like, which further requires energy forpreparing the cooling water.

SUMMARY

One or more embodiments of the present invention offer a method capableof efficiently producing sodium hydroxide and/or chlorine in such a waythat water is supplied to the cathode chamber and overheating of theelectrolytic cell is suppressed without extra energy other than theenergy for electrolytic reaction.

One or more embodiments of the present invention include the following:

[1] A method for producing sodium hydroxide and/or chlorine byelectrolyzing saltwater, comprising using a two-chamber typeelectrolytic cell for saltwater comprising one or more unit cellsequipped with an anode chamber including an anode, a cathode chamberincluding a gas-diffusion cathode, and an ion exchange membranesandwiched by the anode chamber and the cathode chamber, supplyingsaltwater to the anode chamber, and supplying humidifiedoxygen-containing gas to the cathode chamber, wherein each of the unitcells further comprises a humidifying chamber generating the humidifiedoxygen-containing gas that is to be supplied to the cathode chamber, thehumidifying chamber is adjoined to and in heat exchange relation withthe anode chamber or the cathode chamber in one of the unit cells, orthe anode chamber or the cathode chamber in another of the unit cellsadjacent to the one of the unit cells, and the oxygen-containing gas ishumidified by generating water vapor with heat from the anode chamber orthe cathode chamber.

[2] The method according to [1], wherein the humidifying chamber isadjoined to the cathode chamber, and the humidified oxygen-containinggas generated in the humidifying chamber is supplied from thehumidifying chamber to the cathode chamber through at least one openinglocated at a partition between the humidifying chamber and the cathodechamber.

[3] The method according to [2], wherein the at least one openinglocated at the partition between the humidifying chamber and the cathodechamber comprises a single opening.

[4] The method according to [2], wherein the at least one openinglocated at the partition between the humidifying chamber and the cathodechamber comprises a plurality of openings.

[5] The method according to [1], wherein the humidifiedoxygen-containing gas generated in the humidifying chamber is suppliedfrom the humidifying chamber to the cathode chamber through at least oneflow path located outside the humidifying chamber and the cathodechamber.

[6] The method according to [5], wherein the at least one flow pathlocated outside the humidifying chamber and the cathode chambercomprises a single flow path.

[7] The method according to [5], wherein the at least one flow pathlocated outside the humidifying chamber and the cathode chambercomprises a plurality of flow paths.

[8] The method according to any one of [1] to [7], wherein the unitcells are connected with each other in the electrolytic cell, and theunit cells are arranged such that the sequence of the anode chamber, thecathode chamber, and the humidifying chamber is repeated.

[9] A two-chamber type electrolytic cell for saltwater, comprising oneor more unit cells equipped with an anode chamber, a cathode chamber,and an ion exchange membrane sandwiched by the anode chamber and thecathode chamber, wherein the anode chamber includes an anode, and isequipped with an inlet for saltwater as a starting material, an outletfor electrolyzed saltwater, and an outlet for chlorine, the cathodechamber includes a gas-diffusion cathode, and is equipped with an inletfor humidified oxygen-containing gas and an outlet for electrolyticreactant, each of the unit cells further comprises a humidifying chambergenerating oxygen-containing gas that is to be supplied to the cathodechamber, and the humidifying chamber is adjoined to and in heat exchangecontact with the anode chamber or the cathode chamber in one of the unitcells, or the anode chamber or the cathode chamber in another of theunit cells adjacent to the one of the unit cells, and is equipped withan inlet for the oxygen-containing gas.

[10] The electrolytic cell according to [9], wherein the unit cells areconnected with each other in the electrolytic cell, and the unit cellsare arranged such that the sequence of the anode chamber, the cathodechamber, and the humidifying chamber is repeated.

According to one or more embodiments of the present invention, since thehumidifying chamber is adjoined to and in heat exchange relation withthe anode chamber or the cathode chamber, the oxygen-containing gas canbe humidified with heat from the anode chamber or the cathode chamber,and overheating of the electrolytic cell can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-section view of an example of one of unitcells according to one or more embodiments of the present invention.

FIGS. 2A and 2B are schematic cross-section views of examples of theshape of an opening for supplying humidified oxygen-containing gasaccording to one or more embodiments of the present invention.

FIG. 3 is a schematic cross-section view of an example of one of unitcells equipped with a connecting pipe supplying humidifiedoxygen-containing gas according to one or more embodiments of thepresent invention.

FIG. 4 is a schematic cross-section view of an example of a monopolarelectrolytic cell according to one or more embodiments of the presentinvention.

FIG. 5 is a schematic cross-section view of an example of a bipolarelectrolytic cell according to one or more embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, a two-chamber type electrolytic cell for saltwater and amethod for producing sodium hydroxide and/or chlorine using theelectrolytic cell according to one or more embodiments of the presentinvention will be described with reference to the drawings. The presentinvention, however, is not limited by the following drawings and can bealtered in design within a scope in compliance with the intent describedabove and below.

FIG. 1 shows an example of one of unit cells in an electrolytic cellaccording to one or more embodiments of the present invention. Unit cell1 has an anode chamber 3, a cathode chamber 4, and an ion exchangemembrane 2 sandwiched by the anode chamber 3 and the cathode chamber 4.The anode chamber 3 includes an anode 3 a closely adjoining the anodeside of the ion exchange membrane 2. The anode chamber 3 is alsoequipped with an inlet 3 b for saltwater as a starting material at alower part and equipped with an outlet 3 c for electrolyzed saltwaterand chlorine at an upper part. The cathode chamber 4 is equipped with aliquid retention layer 4 b adjoining the cathode side of the ionexchange membrane 2, a gas-diffusion cathode 4 a, and if necessary, agas-diffusion cathode support 4 c and a cushion material 4 d in thisorder.

The unit cell 1 according to one or more embodiments of the presentinvention is equipped with a humidifying chamber 5 separated from thecathode chamber 4 by a partition 6, and the humidifying chamber 5 is inheat exchange relation with the cathode chamber 4. The partition 6exemplified in the drawing has a planar shape as shown in FIG. 2A, andthe space above the partition 6 in whole performs as an opening 7, whichenable humidified oxygen-containing gas to be supplied from thehumidifying chamber 5 to the cathode chamber 4. In addition, the cathodechamber 4 is also equipped with a pressure equalizing line 4 e to keepwater level in the humidifying chamber 5 constant. However, in one ormore embodiments of the present invention, if another measure can keepthe water level in the humidifying chamber 5 constant, the pressureequalizing line 4 e is not required.

In one or more embodiments, water in the humidifying chamber 5 may be incommunication with the outside, or may not be in communication with theoutside. In cases where the water is in communication with the outside,a line can be further provided to introduce water from the outside tothe humidifying chamber and to discharge heated water to the outside(not shown in the figures). In the case where the water is introducedfrom the outside, the flow rate and the temperature of the water can beaccordingly determined such that the water temperature in thehumidifying chamber satisfies the predetermined condition (for example,80° C. or higher). However, in either case, whether the water isintroduced or not introduced from the outside, the only heat produced byelectrolytic reaction may be used to heat the water up to thepredetermined temperature in view of energy efficiency.

In the above unit cell 1, saltwater as a starting material is suppliedfrom the inlet 3 h for saltwater to the anode chamber 3, and at the sametime, oxygen-containing gas is bubbled from an inlet 5 a foroxygen-containing gas into water stored in the humidifying chamber 5 togenerate the humidified oxygen-containing gas (oxygen concentration maybe, for example, 90% or more in some embodiments, and 93% or more inanother embodiment). By supplying the humidified oxygen-containing gasto the cathode chamber 4 and applying an electrical current, chlorine isgenerated art the anode 3 a and sodium hydroxide is generated at thegas-diffusion cathode 4 a. With progression of the electrolytic reactionof saltwater, heat generated at the cathode is conducted to thehumidifying chamber 5, which can heat the water stored in thehumidifying chamber 5 and facilitate vaporization of the water in thehumidifying chamber 5. The following supply of the oxygen-containing gasto the humidifying chamber 5 by means like bubbling can generateoxygen-containing gas including water vapor with an amount approximatelyequal to the saturation amount at the water temperature in thehumidifying chamber. Therefore, without using extra energy other thanthe energy for electrolytic reaction, the efficiency of humidifying theoxygen-containing gas can be improved. Moreover, in the case whereoxygen-containing gas that contains highly concentrated water vapor issupplied from a humidifier located outside the electrolytic cell, whichis disclosed in the Patent Document 1, enough amount of water vaporcannot be supplied because of water condensation in a pipe during beingsupplied. Additionally, especially in an electrolytic cell having someunit cells, each of the unit cells may be supplied with a differentamount of water because the degree of water condensation may vary ineach of the unit cells. On the contrary, in one or more embodiments ofthe present invention, since each of the unit cells is equipped with thehumidifying chamber, enough amount of water can be supplied to each ofthe unit cells without variation of the water amount. Furthermore, byconducting heat of the cathode chamber to the humidifying chamber,overheating of the unit cells, that is, overheating of the electrolyticcell, can be prevented without extra energy for cooling.

In the example of FIG. 1 described above, the humidifying chamber 5 isadjoined to the cathode chamber 4 in the unit cell 1. However, thehumidifying chamber 5 may be adjoined to the anode chamber 3 (asdescribed, the unit cell equipped with the chambers in the sequence ofthe humidifying chamber 5, the anode chamber 3, and the cathode chamber4 is hereinafter referred to as a B-type unit cell, the unit cellequipped with the chambers in the sequence of the anode chamber 3, thecathode chamber 4, and the humidifying chamber 5 is hereinafter referredto as a A-type unit cell.). Even in the case of the B-type unit cell,since the electrolytic reaction at the anode chamber 3 is an exothermalreaction, heat generated by the exothermal reaction can be used to heatthe humidifying chamber 5 to improve the efficiency of generating watervapor. In addition, as described later, more than one B-type unit cellscan be placed next to each other, and in such a case, the humidifyingchamber 5 may be adjoined to the cathode chamber 4 of the adjacent unitcell. In this case, the exothermal reaction in the cathode chamber 4 inthe adjacent unit cell can improve the efficiency of generating watervapor in the humidifying chamber 5.

In one or more embodiments, chlorine generated in the anode chamber 3 isdischarged from the outlet 3 c along with saltwater afterelectrolyzation. Sodium hydroxide generated in the cathode chamber 4 istransformed into aqueous sodium hydroxide having a concentration ofabout 32.0% to 34.0% with electro-osmotic water from the anode chamber 3or moisture in the oxygen-containing gas transferred to the cathodechamber, which runs down the cathode chamber under its weight and isdischarged along with exhaust gas of the oxygen-containing gas from anoutlet 4 g for electrolytic reactant. As described above, since enoughamount of water can be supplied to the cathode in one or moreembodiments of the present invention, the concentration of the aqueoussodium hydroxide can be kept from being too high, and as a result,damage of the gas-diffusion cathode 4 a and the ion exchange membrane 2can be prevented.

In one or more embodiments, the partition 6 in the unit cell 1 may haveat least one opening 7 having various shapes, as long as the partition 6allows the humidified oxygen-containing gas to be communicated from thehumidifying chamber 5 to the cathode chamber 4 through an upper side ofthe partition 6. For example, as shown in FIG. 2B, the partition 6 mayhave a plurality of openings 7 on its upper side. The at least oneopening 7 located at the upper side of the partition 6 may occupy theentire upper side of the partition 6 as shown in FIG. 2A, or may occupya part of the upper side of the partition 6 as shown in FIG. 29.Furthermore, the number of the at least one opening 7 is notparticularly limited and may be one or more. Further, the shape of theat least one opening 7 is not particularly limited.

Moreover, in one or more embodiments, the partition 6 may not have theat least one opening 7, as long as the humidified oxygen-containing gasis allowed to be communicated from the humidifying chamber 5 to thecathode chamber 4. For example, the humidified oxygen-containing gas maybe supplied to the cathode chamber 4 through an external flow path suchas a connecting pipe 8 as shown in FIG. 3. The unit cell 1 in FIG. 3 isthe same as the unit cell in FIG. 1 except that the unit cell 1 in FIG.3 is equipped with the connecting pipe 8 instead of the opening 7 shownin FIG. 1.

In the case where the aforementioned B-type unit cell is used,connecting the humidifying chamber 5 and the cathode chamber 4 by theconnecting pipe 8 as described above enables the humidifiedoxygen-containing gas to be supplied from the humidifying chamber 5 tothe cathode chamber 4. In addition, in the case where more than oneB-type cell is placed next to each other, to enable theoxygen-containing gas to be supplied from the humidifying chamber 5 tothe cathode chamber 4 of the adjacent unit cell, the opening 7 may beformed at the boundary of the humidifying chamber 5 and the cathodechamber 4 of the adjacent unit cell, or the connecting pipe 8 may beconnected to the humidifying chamber 5 and the cathode chamber 4 of theadjacent unit cell.

In the unit cell as described above (including both the A-type unit celland the B-type unit cell; the same applies hereafter), the anode 3 a isnot particularly limited, as long as it is an insoluble anode used forelectrolysis of saltwater. For example, the anode may be such thatcoating of metal oxide including ruthenium oxide, titanium oxide,iridium oxide, or platinum-group metal oxides is applied on a basesubstance having a mesh structure such as expanded metal or fine meshcomposed of metal including titanium.

In one or more embodiments, the ion exchange membrane 2 is notparticularly limited as long as it can be used for electrolysis ofsaltwater, and for example, it can be exemplified by a cation exchangemembrane of perfluorocarbon-type, in which the ion exchange group iscarboxyl acid and/or sulfonic acid.

In one or more embodiments, the gas-diffusion cathode 4 a is notparticularly limited as long as it can be used for electrolysis ofsaltwater by the oxygen cathode method, and it is exemplified by asheet-like triple-layer electrode in which a base material such as metalmesh-like material, carbon cloth, and/or hydrophobic resin is used, areactive layer supported by a hydrophile catalyst is jointed on one sideof the base material, and a water-shedding gas-diffusion layer isjointed on the other side of the base material. The catalyst can beexemplified by silver, platinum, gold, metal oxides, and carbon. Thegas-diffusion cathode may be permeable to liquid, or may not permeableto liquid.

In one or more embodiments, in the cathode chamber 4, absence of liquidbetween the ion exchange membrane 2 and the gas-diffusion cathode 4 amakes it impossible for current to flow therebetween. While liquid canbe retained between the ion exchange membrane 2 and the gas-diffusioncathode 4 by capillary action if the ion exchange membrane 2 and thegas-diffusion cathode 4 are closely attached to each other, the liquidretention layer 4 b may be placed between the ion exchange membrane 2and the gas-diffusion cathode 4 a to retain liquid more certainly. Theliquid retention layer 4 b enables liquid such as aqueous sodiumhydroxide to be uniformly retained between the ion exchange membrane 2and the gas-diffusion cathode 4 a to prevent an increase in currentdensity and voltage. Hydrophilicity and corrosion resistance arerequired for the liquid retention layer because the liquid retentionlayer needs to retain aqueous sodium hydroxide (having a concentrationof about 30% and temperature of about 80° C. to 90° C.) generated byelectrolytic reaction. Therefore, carbon materials such as carbon fibersand a porous structure composed of resin may be used.

An advantage of the two-chamber type method according to one or moreembodiments of the present invention is that voltage can be made smalldue to small electric resistance between the electrodes since the anode,the ion exchange membrane, and the cathode are adjoined to each other.To closely attach the gas-diffusion cathode 4 a to the ion exchangemembrane 2 (if necessary, through the liquid retention layer 4 b), thecushion material 4 d may be placed in a compressed state to generatereactive force, which is utilized to closely attach the gas-diffusioncathode 4 a to the ion exchange membrane 2. In the two-chamber typemethod according to one or more embodiments of the present invention,separated by the ion exchange membrane, liquid, pressure exerted bysaltwater is applied to the anode chamber, and gas pressure is appliedto the cathode chamber. The reactive force of the cushion material 4 dis designed in conformity with the difference between the liquidpressure and the gas pressure. Since the deeper the depth of thesaltwater is, the larger the liquid pressure is, making the reactiveforce of the cushion material at the lower side larger than at the upperside of the cathode chamber enables pressure applied to the ion exchangemembrane or the anode electrode to be uniform. As such a cushionmaterial 4 d, a coiled material or a waved mat material can be used.Since the coiled material has elasticity in the diametrical directionand generates the reactive force in the diametrical direction, the coilaxis can be placed parallel to the back board of the cathode gaschamber, and the reactive force of the cushion material can be designedto be larger at the lower side than at the upper side by selecting thewire diameter of the coil, the diameter of the coil material, and thelaying density of the coil. As to the waved mat material, waved demistermesh in which metal wires are stocking stitched can be used, and thereactive force of the cushion material can be designed to be larger atthe lower side than at the upper side by selecting the diameter of thewires, the number of the wires, and the number of the lamination layersof the mat material.

In one or more embodiments, the gas-diffusion cathode support 4 c can beplaced between the cushion material 4 d and the gas-diffusion cathode 4a, if necessary. The gas-diffusion cathode support 4 c receives thereactive force of the cushion material 4 d to allow the force to beuniformed and transmits the uniformed force to the gas-diffusion cathode4 a and the liquid retention layer 4 b, and farther, the ion exchangemembrane 2. As the gas-diffusion cathode support 4 c, mesh materialssuch as a woven metal wire can be used.

Since both the cushion material 4 d and the gas-diffusion cathodesupport 4 c are placed in the cathode chamber, which is in a highcorrosive environment because of high temperatures and the existence ofhighly concentrated oxygen and highly concentrated sodium hydroxide,nickel or nickel alloy whose nickel content is 20% by weight or more,and silver plating thereof may be used in one or more embodiments.

As the material for the walls constituting the anode chamber 3, titaniumor titanium alloy whose titanium content is 20% by weight or more may beused in one or more embodiments. As the material for the wallsconstituting the cathode chamber 4 and the humidifying chamber 5, nickelor nickel alloy whose nickel content is 20% by weight or more, andsilver plating thereof may be used.

In one or more embodiments of the present invention, more than one ofthe aforementioned unit cells (the A-type unit cells or the B-type unitcells) may be placed next to each other to compose the electrolyticcell. In this case, each of the unit cells may be connected in parallelelectrically to compose a monopolar electrolytic cell, or each of theunit cells may be connected in series electrically to compose a bipolarelectrolytic cell. Hereinafter, the monopolar electrolytic cell and thebipolar electrolytic cell will be explained referring to an example inwhich more than one of the A-type unit cells having the aforementionedopening 7 for the means of communication of the oxygen-containing gasbetween the humidifying chamber 5 and the cathode chamber 4 are placednext to each other. The following example may be applied to anotherexample in which the connecting pipe 8 is used or in which more than oneof the B-type cells are placed next to each other.

FIG. 4 is a schematic cross-section view of an example of a monopolarelectrolytic cell according to one or more embodiments of the presentinvention, in which three of the A-type unit cells having the opening 7are placed next to each other. In the monopolar electrolytic cell 10shown in FIG. 4, more than one of the A-type unit cells (three of theA-type unit cells in the example of the figure), in which theaforementioned anode chamber 3, the cathode chamber 4, and thehumidifying chamber 5 are placed in this sequence, can be arranged suchthat the sequence in each of the unit cells may be alternately reversed,such as the regular sequence (the anode chamber 3, the cathode chamber4, and the humidifying chamber 5 are placed in this sequence), thereverse sequence (the humidifying chamber 5, the cathode chamber 4, andthe anode chamber 3 are placed in this sequence), the regular sequence,and the reverse sequence. The anode electrodes of the unit cells areconnected to an external electric source in parallel electricallyrespectively, and the cathode electrodes of the unit cells are alsoconnected to the external electric source in parallel electrically. Thereference sign 9 shows a water storage tank for adjusting water level inthe humidifying chamber. This example also allows heat of the cathodechamber 4 to be transmitted to the humidifying chamber 5 to humidify theoxygen-containing gas efficiently. In such an aforementioned example, inwhich more than one of the unit cells are placed next to each other suchthat the sequence in each of the unit cells may be alternately reversed,the humidifying chamber 5 of one unit cell (1) may be adjoined to thehumidifying chamber 5 of the next unit cell (2). In this case, onehumidifying chamber 5 may be shared by both the unit cell (1) and theunit cell (2).

FIG. 5 is a schematic cross-section view of an example of a bipolarelectrolytic cell according to one or more embodiments of the presentinvention, in which four of the A-type unit cells having the opening 7are placed next to each other. In the bipolar electrolytic cell 20 shownin FIG. 5, more than one of the unit cells 1 (four of the unit cells 1in the example of the figure), each of which has the anode chamber 3 andthe cathode chamber 4 internally having the humidifying chamber 5, arearranged such that the sequence of the anode chamber 3, the cathodechamber 4, and the humidifying chamber 5 is repeated. In the bipolarelectrolytic cell 20, the anode electrode 3 a in one unit cell (1) iscapable of being electrically conducted to the cathode electrode 4 a inthe next unit cell (2) (not shown in the figure), and the cathodeelectrode 4 a at one end and the anode electrode 3 a at the other endare connected to an external electric source respectively to connecteach of the unit cells in series electrically. Each of the inlets 3 hfor saltwater of the unit cells, each of the outlets 3 c forelectrolyzed saltwater and chlorine of the unit cells, each of theinlets 5 a for oxygen-containing gas of the unit cells, each of waterinlets 5 b of the unit cells, each of the outlets 4 g for electrolyticreactant of the unit cells, and each of the pressure equalizing lines 4e of the unit cells are respectively connected to one another by pipes,and the water inlets 5 b and the pressure equalizing lines 4 e areconnected to the water storage tank 9. The mechanism of the electrolyticreaction in each of the unit cells of the bipolar electrolytic cell 20is the same as in the aforementioned unit cells. However, because of thearrangement of the unit cells, Each of the humidifying chambers 5 isadjoined not only to the cathode chamber 4 in the same unit cell butalso to the anode chamber 3 in the next unit cell. Therefore, thehumidifying chamber 5 can use heat generated by electrolytic reaction inboth the anode chamber 3 and the cathode chamber 4 for humidification,which results in the increase of the heat efficiency in humidification.In addition, since the heat generated in the anode chamber 3 istransferred to the humidifying chamber 5, the anode chamber 3 can becooled at the same time.

Moreover, in the case where more than one of the B-type unit cells(having the sequence of the humidifying chamber, the anode chamber, andthe cathode chamber) are arranged regularly without alternatelyreversing the sequence of each of the unit cells to compose a bipolarelectrolytic cell such as the example shown in FIG. 5, the humidifyingchamber 5 is sandwiched by the anode chamber 3 and the cathode chamber4. In this case, the humidifying chamber 5 can also use heat generatedin both the anode chamber 3 and the cathode chamber 4 duringhumidification.

The present application claims priority based on Japanese PatentApplication No. 2017-068057 filed on Mar. 30, 2017. All the contentsdescribed in Japanese Patent Application No. 2017-068057 filed on Mar.30, 2017 are incorporated herein by reference.

EXAMPLES

Hereinafter, one or more embodiments of the present invention are morespecifically described with reference to examples. The presentinvention, however, is not limited by the following examples but canalso be absolutely carried out with appropriate changes to the exampleswithin a scope in compliance with the intent described above and later,and all the changes are to be encompassed within a technical scope ofthe present invention.

Example 1

Five of the unit cells shown in FIG. 1 (except not having agas-diffusion cathode support) were arranged such that the sequence ofan anode chamber, a cathode chamber, and a humidifying chamber wasrepeated in this sequence, and were connected to each other in serieselectrically to compose a bipolar two-chamber type electrolytic cell forsaltwater. DSE manufactured by De Nora Permelec Ltd. (insoluble metal inwhich metal base substance is coated with platinum-group metal or oxidesthereof as a main component) was used as an anode electrode; gas-liquidtransmissive carbon-silver electrode (GDE2013) manufactured by De NoraPermelec Ltd. was used as an cathode electrode; 4403D manufactured byAsahi Kasei Chemicals Corporation was used as an ion exchange membrane;carbon fiber woven fabric, the thickness of which is 0.45 mm, was usedas a liquid retention layer; and silver-plated nickel wire in spiralshape was used as a cushion material.

Saltwater having a concentration of 218 g/L and a temperature of 53.8°C. was supplied to the anode chamber at the rate of 183 L/m²/h. Waterwas stored in the humidifying chamber, to which 1.5 times thetheoretical requisite moles of oxygen-containing gas (corresponds to“oxygen-containing gas supplied to electrolytic cell” shown in the belowtable 1) having a temperature of 25° C. and a concentration of 93.0% wassupplied by bubbling. The temperature of the humidifying chamber was84.0° C., and therefore, at the time when being supplied to the cathodechamber, the temperature of the humidified oxygen-containing gas wasabout 84.0° C. The saltwater was electrolyzed at the current density of5.65 kA/m², and each value was measured after ten days of theelectrolyzation.

Comparative Example 1

Except not having the humidifying chamber in a unit cell, five of thesame unit cells as Example 1 having the same material of the anodeelectrode, the cathode electrode, the ion exchange membrane, etc. andthe same size of the cathode chamber, the anode chamber, etc. werearranged such that the sequence of the anode chamber, and the cathodechamber is repeated in this sequence, and were connected to each otherin series electrically to compose a conventional bipolar two-chambertype electrolytic cell for saltwater (not shown in the figures).

Saltwater having a concentration of 219 g/L, and a temperature of 51.4°C. was supplied to the anode chamber at the rate of 183 μm²/h. Thecathode chamber of each of the unit cells was connected to a humidifierprepared outside the electrolytic cell. In the humidifier, 1.5 times thetheoretical requisite moles of oxygen-containing gas having aconcentration of 93.0% was bubbled into the water (25° C.) in thehumidifier to generate humidified oxygen-containing gas having atemperature of 25° C., which was supplied to the cathode chamber at thesame temperature. The saltwater was electrolyzed at the current densityof 5.65 kA/m², and each value was measured after ten days of theelectrolyzation. Being different from Example 1, Comparative Example 1did not have the humidifying chamber in the unit cell and the humidifiedoxygen-containing gas was supplied from the external humidifier, andtherefore, the meaning of “oxygen-containing gas supplied toelectrolytic cell” and “oxygen-containing gas supplied to cathodechamber” shown in the below table 1 are identical in meaning (the sameapplies to the following Comparative Examples 2 to 4).

Comparative Example 2

In the same manner as in Comparative Example 1 except that the watertemperature of the external humidifier in Comparative Example 1 wasaltered to 84° C., and that humidified oxygen-containing gas generatedat 84° C. was supplied to the cathode chamber at the same temperature(heat input rate to the humidifier was about 5.2 MJ/m²/h), each valuewas measured after ten days of the electrolyzation.

Comparative Example 3

With the same composition as in Comparative Example 2, additionally,heat-retention around the pipe connecting the humidifier and the anodechamber of each of the unit cells was improved to prevent thetemperature of the humidified oxygen-containing gas from decreasing, andeach value was measured after ten days of the electrolyzation. The heatinput rate to the humidifier was about 5.2 MJ/m²/h, which was the sameas in Comparative Example 2.

Example 2

The same electrolytic cell as in Example 1 was operated for 300 days,after which each value was measured.

Comparative Example 4

The same electrolytic cell as in Comparative Example 1 was operated for300 days, after which each value was measured.

The measurement results of the Examples and the Comparative Examples areshown in Table 1 and Table 2. Table 2 shows both the average value offive of the unit cells and the difference between the average value andeach value of five of the unit cells in the concentration of generatedsodium hydroxide and current efficiency.

TABLE 1 Oxygen-containing gas supllied to Liquid in anode electrolysiscell Current Supplied Saline water compartment Multiple of densityAmount Concentration Temperature Concerntration TemperatureConcentration theoretical Temperature (kA/m²) (L/m²/h) (g/L) (° C.)(g/L) (° C.) (%) amount (° C.) Example 1 5.65 183 218 53.8 173 84.0 93.0×1.5 25.0 Comparative 5.65 183 219 51.4 174 84.0 93.0 ×1.5 25.0 Example1 Comparative 5.65 183 219 47.0 174 84.0 93.0 ×1.5 84.0 Example 2Comparative 5.65 183 219 47.0 174 84.0 93.0 ×1.5 84.0 Example 3 Example2 5.65 183 218 53.3 173 84.0 93.0 ×1.5 25.0 Comparative 5.65 183 21951.0 174 84.0 93.0 ×1.5 25.0 Example 4 Oxygen-containing gas supplied toAverage cathode Temperature Temperature concentration compartment Cellin humidifying Temperature of exhaust of generated Current Temperaturevoltage compartment of catode gas NaOH efficiency (° C.) (V) (° C.) (°C.) (° C.) (%) (%) Example 1 84.0 2.30 84.0 82.0 82.0 32.2 96.5Comparative 25.0 2.32 — 75.0 75.0 34.6 96.5 Example 1 Comparative 84.02.30 — 82.0 82.0 32.2 96.4 Example 2 Comparative 84.0 2.30 — 82.0 82.032.2 96.5 Example 3 Example 2 84.0 2.35 84.0 82.0 82.0 32.2 96.3Comparative 25.0 2.43 — 75.0 75.0 34.6 96.0 Example 4

TABLE 2 Concentration of generated NaOH Current efficiency AverageAverage (%) #1 #2 #3 #4 #5 (%) #1 #2 #3 #4 #5 Example 1 32.2 −0.2% +0.1%+0.1% +0.2% −0.2% 96.5 −0.2% +0.1%    0% +0.2% −0.1% Comparative 34.6−0.2% +0.2% +0.1% +0.1% −0.2% 96.5 −0.3% +0.1% +0.1%    0% +0.1% Example1 Comparative 32.2 +0.5% −0.2% −0.4% −0.2% +0.3% 96.4 −0.4% +0.2% +0.3%+0.2% −0.3% Example 2 Comparative 32.2 −0.1% +0.2% +0.2%    0% −0.3%96.5 −0.2% +0.2% +0.1%    0% −0.1% Example 3 Example 2 32.2 −0.1% +0.1%   0% +0.2% −0.2% 96.3 −0.2% +0.1%    0% +0.2% −0.1% Comparative 34.6   0% +0.2% +0.1% −0.1% −0.2% 96.0 −0.3%  +0% +0.2% +0.2% −0.1% Example4

In Example 1, due to the reaction heat, the temperature of thehumidifying chamber was equivalent to the temperature of the anodechamber, and the concentration of generated sodium hydroxide was 32.2%,not too high, which shows that enough amount of water vapor was supplied(Table 1). In addition, variation in the concentration of generatedsodium hydroxide and in current efficiency in each of five unit cellscould be made small, which shows that the variation in the amount of thewater vapor supplied to the anode chamber of each of the unit cells wassmall (Table 2). Moreover, Example 2, in which the electrolyzation wasoperated longer than in Example 1, showed good current efficiency of96.3% even after 300 days, as well as good results in other valuesalmost the same as in Example 1. Since enough amount of water vaporcould be supplied in Example 2, low concentration of generated sodiumhydroxide could be maintained, and since damage of the gas-diffusioncathode was prevented in Example 2, the difference in voltage of thegas-diffusion cathode after 300 days of electryzation was as small as 45mV on average. The differences in voltage of the gas-diffusion cathodein each of the unit sells were 78 mV, 15 mV, 45 mV, 33 mV, and 54 mVrespectively.

On the other hand, in Comparative Example 1, in which humidifiedoxygen-containing gas was supplied from the external humidifier, sincethe temperature of the external humidifier was 25.0° C., the pressure ofwater vapor in the gas was low, and the concentration of generatedsodium hydroxide was as high as 34.6% which shows that the suppliedamount of water vapor was insufficient (Table 1).

Comparative Example 2 was an example in which the temperature of theexternal humidifier was altered to 84° C. to increase the water vaporpressure in the oxygen-containing gas, which required energy to raisewater temperature in the external humidifier. The average concentrationof generated sodium hydroxide was 32.2% which means that enough amountof water vapor could be supplied on the average, however, as shown inTable 2, the variation in both the concentration of sodium hydroxide andcurrent efficiency of each unit cell became large. The reason of this isconsidered that water was condensed in the process where theoxygen-containing gas was supplied from the external humidifier to thecathode chamber of each of the unit cells, and the degree of thecondensation was different in each of the unit cells. In addition, sincethe oxygen-containing gas of high temperature was supplied from outsidethe electrolytic cell, the saltwater supplied to the anode electrode wasrequired to have a low temperature to prevent the electrolytic cell fromoverheating (while the temperature of the supplied saltwater in Example1 was 0.53.8° C., which is within the usual range of the temperature insaltwater electrolysis plants, the temperature of the supplied saltwaterin Comparative Example 2 was 47.0° C.), and thus, extra energy wasrequired for cooling the supplied saltwater.

Comparative Example 3 was an example in which heat-retention of the pipefrom the external humidifier in Comparative Example 2 was improved, andrequired extra energy for heating in the external humidifier, which isthe same as in Comparative Example 2. In Comparative Example 3, watercondensation was suppressed in the pipes, and as a result, thevariations in the concentration of the generated sodium hydroxide andthe current efficiency of each of the unit cells could be made small,however, extra energy for cooling the supplied saltwater was required inthe same manner as in Comparative Example 2.

Comparative Example 4 was an example in which the electrolytic cell wasoperated for 300 days in the same condition as in Comparative Example 1,and the difference in the voltage of the gas-diffusion cathode after 300days of electrolyzation was 108 mV on average of five of the unit cells,which was much higher than in Example 2, and current efficiency was96.0%, which was lower than in Example 2. The reason of this isconsidered that as the same as in Comparative Example 1, theconcentration of generated sodium hydroxide was 34.6% in ComparativeExample 4, which was 2% or higher than the concentration of sodiumhydroxide of 32.2% in Examples 1 and 2, and as a result, thegas-diffusion cathode was damaged. The differences in voltage of thegas-diffusion cathode in each of the unit sells were 123 mV, 66 mV, 114mV, 108 mV, and 129 mV respectively.

Although the disclosure has been described with respect to only alimited number of embodiments, those skilled in the art, having benefitof this disclosure, will appreciate that various other embodiments maybe devised without departing from the scope of the present invention.Accordingly, the scope of the invention should be limited only by theattached claims.

DESCRIPTION OF REFERENCE SIGNS

-   -   1: unit cell    -   2: ion exchange membrane    -   3: anode chamber    -   3 a: anode electrode    -   4: cathode chamber    -   4 a: gas-diffusion cathode    -   5: humidifying chamber    -   6: partition    -   7: opening    -   8: connecting pipe    -   10: monopolar electrolytic cell    -   20: bipolar electrolytic cell

What is claimed is:
 1. A method for producing sodium hydroxide and/orchlorine by electrolyzing saltwater, the method comprising: supplyingsaltwater to an anode chamber of a unit cell in a two-chamber typeelectrolytic cell; humidifying oxygen-containing gas in a humidifyingchamber of the unit cell; and supplying humidified oxygen-containing gasgenerated in the humidifying chamber to a cathode chamber of the unitcell, wherein the unit cell comprises: the anode chamber including ananode; the cathode chamber including a gas-diffusion cathode; an ionexchange membrane sandwiched by the anode chamber and the cathodechamber; and the humidifying chamber, wherein the two-chamber typeelectrolytic cell comprises one or more unit cells, wherein thehumidifying chamber is adjoined to and in heat exchange relation withthe anode chamber or the cathode chamber in the unit cell, or isadjoined to and in heat exchange relation with an anode chamber or acathode chamber in another unit cell adjacent to the unit cell, andwherein the oxygen-containing gas is humidified by generating watervapor with heat from the anode chamber or the cathode chamber adjoinedto the humidifying chamber.
 2. The method according to claim 1, whereinthe humidifying chamber is adjoined to the cathode chamber, and whereinthe humidified oxygen-containing gas generated in the humidifyingchamber is supplied from the humidifying chamber to the cathode chamberthrough at least one opening located at a partition between thehumidifying chamber and the cathode chamber.
 3. The method according toclaim 2, wherein the at least one opening located at the partitionbetween the humidifying chamber and the cathode chamber comprises asingle opening.
 4. The method according to claim 2, wherein the at leastone opening located at the partition between the humidifying chamber andthe cathode chamber comprises a plurality of openings.
 5. The methodaccording to claim 1, wherein the humidified oxygen-containing gasgenerated in the humidifying chamber is supplied from the humidifyingchamber to the cathode chamber through at least one flow path locatedoutside the humidifying chamber and the cathode chamber.
 6. The methodaccording to claim 5, wherein the at least one flow path located outsidethe humidifying chamber and the cathode chamber comprises a single flowpath.
 7. The method according to claim 5, wherein the at least one flowpath located outside the humidifying chamber and the cathode chambercomprises a plurality of flow paths.
 8. The method according to claim 1,wherein the two-chamber type electrolytic cell comprises at least twounit cells, wherein the at least two unit cells are connected with eachother, and wherein the at least two unit cells are arranged such thatthe sequence of the anode chamber, the cathode chamber, and thehumidifying chamber is repeated.
 9. A two-chamber type electrolytic cellfor saltwater comprising one or more unit cells, each unit cellcomprising: an anode chamber; a cathode chamber; an ion exchangemembrane sandwiched by the anode chamber and the cathode chamber; and ahumidifying chamber, wherein the anode chamber comprises an anode, andis equipped with an inlet for saltwater as a starting material, anoutlet for electrolyzed saltwater, and an outlet for chlorine, whereinthe cathode chamber comprises a gas-diffusion cathode, and is equippedwith an inlet for humidified oxygen-containing gas and an outlet forelectrolytic reactant, wherein the humidified oxygen-containing gas isgenerated in the humidifying chamber and supplied to the cathodechamber, wherein the humidifying chamber is adjoined to and in heatexchange relation with the anode chamber or the cathode chamber in theunit cell, or is adjoined to and in heat exchange relation with an anodechamber or a cathode chamber in another unit cell adjacent to the unitcell, and wherein the humidifying chamber is equipped with an inlet forthe oxygen-containing gas.
 10. The electrolytic cell according to claim9, wherein the two-chamber type electrolytic cell comprises at least twounit cells, wherein the at least two unit cells are connected with eachother, and wherein the at least two unit cells are arranged such thatthe sequence of the anode chamber, the cathode chamber, and thehumidifying chamber is repeated.